Room pressure controlling system

ABSTRACT

A room pressure controlling system having a local exhaust valve, a supply air valve, a common exhaust air valve, controllers and a differential pressure sensor. The controller calculates a correction control output value for the valve operated as the room pressure controlling valve, which is either the supply air valve or the common exhaust air valve, based on a setting value and a room pressure measured by the differential pressure sensor. The controller evaluates whether or not the supply airflow rate and/or the exhaust airflow rate is changing, and if an airflow rate is changing, emphasizes rapid responsiveness of the room pressure control than a reduction in the frequency of actuation of the room pressure controlling valve, if the airflow rate is stable, the controller emphasizes the reduction in the frequency of actuation of the room pressure controlling valve than the rapid responsiveness of the room pressure control.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2011-107961, filed May 13, 2011, which isincorporated herein by reference.

FIELD OF TECHNOLOGY

The present invention relates to a room pressure controlling system formaintaining a constant room pressure through controlling the supplyairflow and exhaust airflow of a room.

BACKGROUND

In chemical experiments, during the process of the external operations,often biochemical substances that are harmful to humans are produced.Fume hoods are used as one type of equipment to prevent thesebiochemical substances from being diffused into a room and to preventthem from coming into contact with the human body. Typically, fume hoodsare provided with an enclosure with a sash that can be opened eithervertically or horizontally, where an operator in the laboratory canaccess the inside of the enclosure through the sash. So that theoperator will not be exposed to harmful biochemical substances duringthe operations using the fume hood, the enclosure is connected to alocal exhaust duct that removes the biochemical substances.

The room pressure controlling system is a system for maintaining aconstant pressure within a room so that when biochemical substances arehandled within a fume hood, the airflow rate of the local exhaust ductwill be adjusted so as to maintain a specific speed for the planarairflow rate within the sash plane so that there will be no backflow ofbiochemicals into the room, so that biochemical substances will not leakout of the room and that contamination, and like, will not leak into theroom (See, for example, Japanese Unexamined Patent ApplicationPublication H9-201540). FIG. 8 is a diagram illustrating the structureof a conventional room pressure controlling system. The room pressurecontrolling system comprises: a fume hood 101 that is disposed withinthe room 100; a local exhaust duct 102 that is connected to the fumehood 101; a supply air duct 103 for supplying supply air to the room100; a common exhaust duct 104 for the air of the room 100; a localexhaust air valve EXV for regulating the airflow rate of the localexhaust duct 102; a supply air valve MAV for regulating the airflow rateof the supply air duct 103; a common exhaust air valve GEX forregulating the airflow rate of the common exhaust duct 105; a controller105 for controlling the local exhaust air valve EXV; a controller 106for controlling the supply air valve MAV; a controller 107 forcontrolling the common exhaust air valve GEX; and communication lines108 for connecting together the various controllers 105-1, 106, and 107.The fume hood 101 is provided with a sash 111 that can be opened andclosed, and a sash sensor 112 for detecting the degree of opening of thesash 111.

In this type of room pressure controlling system, in order to maintainthe pressure of the room 100 at the setting value, the degrees ofopening of the supply air valve MAV and the common exhaust air valveGEX, and of the local exhaust air valve EXV, are controlled so that thesupply airflow rate of the supply air duct 103, the exhaust airflow rateof the common exhaust duct 104, and the local exhaust airflow rate ofthe local exhaust duct 102 will satisfy the relationship of “Supplyairflow rate=common exhaust airflow rate+local exhaust airflowrate+offset airflow rate.” Moreover, in recent years a PCV (pressurecontrol valve) function, for performing stabilized pressure control byadjusting the degree of opening of the PCV valve based on a pressuredifferential by measuring the pressure differential between the insideand the outside of the room has been added as well. This PCV function isachieved through causing the room pressure controlling operations to beperformed as well in addition to the actual functions of either thesupply air valve MAV or the common exhaust air valve GEX.

Conventionally, the valve that has handled the PCV function has beenestablished unchangingly at the time of system configuration, causing itto be operated more frequently then the other valves in order to performthe fine adjustment operations for the room pressure, which isproblematic in that the frequency of actuation is higher, reducing theservice life. When a valve that handles a PCV function fails, it tendsto cause large failures in the room pressure control.

The present invention was created in order to solve the problems setforth above, and the object thereof is to provide a room pressurecontrolling system able to extend the service life of a valve that isprovided with a PCV function and to be able to extend the up-time, andthe time between maintenance.

SUMMARY

The room pressure controlling system according to examples of thepresent invention include a supply air valve for regulating an airflowrate for supply air that is blown into an applicable room; a commonexhaust air valve for regulating an airflow rate of exhaust air that isdrawn from the applicable room; airflow rate controlling means foroutputting a control output value for a supply air valve and a controloutput value for a common exhaust air valve, so as to cause thedifference between the supply airflow rate that is regulated by thesupply air valve and the exhaust airflow rate that is regulated by thecommon exhaust valve to match a specific setting value; differentialpressure measuring means for measuring a room pressure that is apressure difference between an applicable room and a specific referenceroom; correction output calculating means for calculating a correctioncontrol output value for a valve that is operated as a room pressurecontrolling valve, which is either the supply air valve or the commonexhaust air valve, based on a deviation between a room pressure measuredby the differential pressure measuring means and a specific settingvalue; summing means for summing the control output value correspondingto the valve that is used as the room pressure controlling valve and thecorrection control output value, and outputting the result to the roompressure controlling valve; and flow rate stability evaluating means forevaluating whether or not the supply airflow rate and/or the exhaustairflow rate is changing; wherein when it has been evaluated by theairflow rate stability evaluating means that the airflow rate ischanging, the correction output calculating means perform a controlcalculation emphasizing rapid responsiveness of the air pressure controlover the reduction of the frequency of actuation of the room pressurecontrolling valve, and if the evaluation is that the airflow rate isstable, the correction output calculating means perform a controlcalculation emphasizing the reduction in the frequency of actuation ofthe room pressure controlling valve over the instant responsiveness ofthe room pressure control.

Moreover, an example of a room pressure controlling system according tothe present invention further have room pressure stability evaluatingmeans for evaluating whether or not the room pressure measured by thedifferential pressure measuring means is stable; where when it has beenevaluated by the airflow rate stability evaluating means that theairflow rate is stable and it has been evaluated by the room pressurestability evaluating means that the room pressure is stable, thecorrection output calculating means continue to output the correctioncontrol output value that was outputted in the immediately previouscalculating period until a time of outputting a correction controloutput value in a calculating period that is after the currentcalculating period. Moreover, this example of a room pressurecontrolling system according to the present invention further hascontrol parameter storing means for storing a plurality of controlparameters for use in calculation processes by the correction outputcalculating means, where when it has been evaluated by the airflow ratestability evaluating means that the airflow rate is changing, thecorrection output calculating means read out and use, from the controlparameter storing means, a control parameter that emphasizes rapidresponsiveness of room pressure control more greatly than a reduction inthe frequency of actuation of the room pressure controlling, valve, andif it has been evaluated that the airflow rate is stable, then thecorrection output calculating means read out and use, from the controlparameter storing means, a control parameter that emphasizes a reductionin the frequency of actuation of the room pressure controlling valvemore greatly than the rapid responsiveness of the room pressure control.

Moreover, the example of a room pressure controlling system furtherincludes calculating period storing means for storing a plurality ofcalculating periods used in the calculating processes of the correctionoutput calculating means, where when it has been evaluated by theairflow rate stability evaluating means that the airflow rate ischanging, the correction output calculating means read out and use, fromthe calculating period storing means, a value for the calculating periodthat emphasizes rapid responsiveness of room pressure control moregreatly than a reduction in the frequency of actuation of the roompressure controlling valve, and if it has been evaluated that theairflow rate is stable, then the correction output calculating meansread out and use, from the calculating period storing means, a value forthe calculating period that emphasizes a reduction in the frequency ofactuation of the room pressure controlling valve more greatly than therapid responsiveness of the room pressure control.

Moreover, this example of a room pressure controlling system also has afume hood that is equipped within the applicable room; and a localexhaust valve for regulating the exhaust airflow rate of the fume hood;and local exhaust airflow rate regulating means for controlling thelocal exhaust air valve so that the planar air speed of a sash plane ofthe fume hood is a specified value; where the airflow rate controllingmeans output a control output value for the supply air valve and acontrol output value for the common exhaust air valve so that thedifference between the supply airflow rate that is regulated by thesupply air valve and the exhaust airflow rate that is regulated by thelocal exhaust air valve and the common exhaust air valve matchs aspecific setting value.

The examples of the present invention make it possible to reduce thefrequency of actuation of the room pressure controlling valve whilemaintaining a constant room pressure, through changing the calculationsfor the control of the room pressure for when the airflow rate ischanging and for when the airflow rate is stable. It is possible toextend the service life of the valve, while using an inexpensive valve,thereby enabling a decrease in the system cost.

Moreover, it is possible to stop the operation of the room pressurecontrolling valve by suspending the output of the correction controllingoutput value and suspending the room pressure control when the airflowrate is stable and the room pressure is stable, making it possible tofurther reduce the frequency of actuation of the room pressurecontrolling valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a structure of a room pressurecontrolling system according to an example according to the presentinvention.

FIG. 2 is a block diagram illustrating an example of a structure for acontroller for a local exhaust according to another example.

FIG. 3 is a block diagram illustrating an example of a structure for acontroller for supply air according to a further example.

FIG. 4 is a block diagram illustrating an example of a structure for acontroller for a common exhaust according to yet another example.

FIG. 5 is a diagram illustrating one example of a daytime design airflowrate value and a nighttime design airflow rate value.

FIG. 6 is a flowchart for explaining the PCV controlling operation in aroom pressure controlling system according to a form of embodimentaccording to the present invention.

FIG. 7 is a diagram illustrating one example of PID parameters when theairflow rate is changing and PID parameters when the airflow rate isstable.

FIG. 8 is a diagram illustrating a conventional structure for a roompressure controlling system.

DETAILED DESCRIPTION

Forms for carrying out the present invention are explained below inreference to the figures. FIG. 1 is a diagram illustrating a structurefor a room pressure controlling system according to an example, wherestructures that are identical to those of FIG. 8 are assigned identicalcodes. The room pressure controlling system according to the presentexample is structured from a fume hood 101 that is disposed within theroom 100; a local exhaust ducts 102; a supply air duct 103; a commonexhaust duct 105; a local exhaust air valve EXV; a supply air valve MAV;a common exhaust air valve GEX; controllers 105, 106, and 107; acommunication line 108; a differential pressure sensor 109 for measuringthe pressure difference between the room 100 and a specific referencechamber (a space outside of the room 100 in the present example); and aroom pressure monitor 110 for checking the pressure difference.

FIG. 2 is a block diagram illustrating a structural example of acontroller 105; FIG. 3 is a block diagram illustrating a structuralexample of a controller 106; and FIG. 4 is a block diagram illustratinga structural example of a controller 107.

The controller 105 has an exhaust airflow rate controlling portion 200for controlling the local exhaust air valve EXV.

The controller 106 has a supply airflow rate controlling portion 201 forcontrolling the supply air valve MAV.

The controller 107 has an exhaust airflow rate controlling portion 202for controlling a common exhaust valve GEX; an air flow rate changingportion 203 for changing gradually a supply airflow rate and an exhaustairflow rate at the time of a specific airflow rate switchingcontrolling operation; an airflow rate stability evaluating portion 204for evaluating whether or not the supply airflow rate and/or the exhaustairflow rate is changing; a room pressure stability evaluating portion205 for evaluating whether or not the room pressure measured by thedifferential pressure sensor 109 is stable; a correction outputcalculating portion 206 for calculating, based on a room pressuremeasured by the differential pressure sensor 109 and on a specificsetting value, a correction control output value for a valve that isoperated as a room pressure controlling valve, which is either thesupply air valve MAV or the common exhaust air valve GEX; a summingportion 207 for summing the control output value corresponding to thevalve that is operated as the room pressure controlling valve with thecorrection control output value, and for outputting the sum value to theroom pressure controlling valve; a control parameter storing portion 208for storing a plurality of control parameters used in the calculationprocesses of the correction output calculating portion 206; and acalculating period storing portion 209 for storing a plurality ofcalculating periods that are used in the calculation processes in thecorrection output calculating portion 206.

The exhaust airflow rate controlling portion 200 of the controller 105structures local exhaust airflow rate regulating means. The supplyairflow rate controlling portion 201 of the controller 160, and theexhaust airflow rate controlling portion 202 and airflow rate changingportion 203 of the controller 107 structure the airflow rate controllingmeans.

Note that while in the present example, an airflow rate changing portion203, an airflow rate stability evaluating portion 204, a room pressurestability evaluating portion 205, a correction output calculatingportion 206, a summing portion 207, and a control parameter storingportion 208 are provided in the controller 107, there is no limitationthereto, but rather the airflow rate changing portion 203, the airflowrate stability evaluating portion 204, the room pressure stabilityevaluating portion 205, the correction output calculating portion 206,the summing portion 207, and the control parameter storing portion 208may be provided in another controller, or may be provided in a centralmonitoring device, not shown.

The airflow rate balance controlling operation during normal operationof the room pressure controlling system is explained next. Here thesupply airflow rate that is blown out from the supply air duct 103 isdefined as Vmav, the airflow rate of the exhaust that is drawn out bythe common exhaust duct 104 is defined as Vgex, and the airflow rate ofthe exhaust that is drawn out by the local exhaust duct 102 is definedas Vexv.

The exhaust airflow rate controlling portion 200 of the controller 105establishes the airflow rate Vexv based on the sash opening area of thefume hood 102 so that the planar airflow rate in the plane of the sashis a specified value (normally 0.5 m/s), and controls the degree ofopening of the local exhaust air valve EXV so that the exhaust airflowrate of the local exhaust duct 101 is Vexv. Note that the sash openingarea of the fume hood 101 can be established by multiplying together theknown sash width by the height of the opening portion of the sash 112,which can be calculated from the degree of sash opening detected by thesash sensor 112.

The exhaust airflow rate controlling portion 202 of the controller 107controls the degree of opening of the common exhaust air valve GEX toreduce the airflow rate Vgex by the amount of change in the exhaustairflow rate Yexv depending on the degree of opening of the sashes, sothat the total exhaust airflow rate (Vgex+Vexv) is constant, to producea control output value so that the exhaust airflow rate of the commonexhaust duct 104 will go to Vgex.

The supply airflow rate controlling portion 201 of the controller 106controls the degree of opening of the supply air valve MAV bydetermining an airflow rate Vmav such that at least a minimum airflowrate is always be blown out so as to satisfy a minimum exchange airflowrate for the room 100, and producing a control output value so that thesupply airflow rate of the supply air duct 103 goes to Vmav. Vmav is setso as to be no less than the minimum exchange airflow rate, in order tomaintain the minimum exchange airflow rate of the room 100.

Through the method of setting the airflow rates as set forth above,Equation (1) is satisfied when the fume hood 101 not is used (that is,when the sash 111 is completely closed):Vmav=Vgex+α  (1)

The constant α is an offset airflow rate for not only determining therate with which air leaks from the room 100, but also for determiningwhether the room 100 is to be caused to be at positive pressure ornegative pressure.

In addition, when the fume hood 101 is used, then Equation (2) issatisfied:Vmav+Vgex+Vexv+α  (2)

Note that if for example, the exhaust airflow rate Vexv were to go tothe maximum airflow rate (Vexv)max then the exhaust airflow ratecontrolling portion 202 of the controller 107 would attempt to balancethe airflow rates by reducing the airflow rate Vgex; however, even if anattempt were made to balance the airflow rate by an operation to reducethe airflow rate Vgex alone, if the degree of opening of the commonexhaust air valve GEX has reached 0%, then the airflow rate Vgex cannotbe reduced any further. In such a case, the supply airflow ratecontrolling portion 201 of the controller 106 would regulate the airflowrate Vmav so as to satisfy Equation (3):Vmav=Vgex+(Vexv)max+α  (3)

The airflow rate balance controlling operations described above vary thesupply airflow rate Vmav and the exhaust airflow rate Vgex in accordancewith the variation when there is variation in the local exhaust airflowrate Vexv accompanying opening or closing of the sash 111 of the fumehood 101.

The airflow rate balance controlling operations described above vary thesupply airflow rate Vmav and the exhaust airflow rate Vgex in accordancewith the variation when there is variation in the local exhaust airflowrate Vexv accompanying opening or closing of the sash 111 of the fumehood 101. This change in the airflow rate, on weekdays, is performedevery day. In the example of switching the time band from daytime tonighttime, both the supply airflow rate Vmav and the exhaust airflowrate Vgex are gradually decreased, and in the example of switching thetime band from nighttime to daytime, both the supply airflow rate Vmavand the exhaust airflow rate Vgex are gradually increased.

Explaining the airflow rate switch controlling operation morespecifically, when switching the time band from daytime to nighttime,the airflow rate changing portion 203 of the controller 107 sendsinstructions to the controller 106 to gradually decrease the supplyairflow rate Vmav from the daytime airflow rate value that has been setin advance for the daytime time band. The supply airflow ratecontrolling portion 201 of the controller 106 controls the degree ofopening of the supply air valve MAV by outputting a control output valueto produce the supply airflow rate Vmav that has been directed by theairflow rate changing portion 203. Moreover, the airflow rate changingportion 203 sends a control output value for the exhaust so as todecrease the exhaust airflow rate Vgex in accordance with the decreasein the supply airflow rate Vmav. At this time, the exhaust airflow rateVgex is determined so as to satisfy Equation (1) or Equation (2). Theairflow rate changing portion 203 performs the changing of the airflowrate until the supply airflow rate Vmav reaches the nighttime designairflow rate value that has been set in advance for the nighttime timeband.

On the other hand, when switching the time band from nighttime todaytime, the airflow rate changing portion 203 sends instructions to thecontroller 106 to gradually increase the supply airflow rate Vmav fromthe nighttime airflow rate value. The supply airflow rate controllingportion 201 of the controller 106 controls the degree of opening of thesupply air valve MAV by outputting a control output value to produce thesupply airflow rate Vmav that has been directed by the airflow ratechanging portion 203. Moreover, the airflow rate changing portion 203sends a control output value for the exhaust so as to increase theexhaust airflow rate Vgex in accordance with the increase in the supplyairflow rate Vmav. At this time, the exhaust airflow rate Vgex isdetermined so as to satisfy Equation (1) or Equation (2). The airflowrate changing portion 203 performs the changing of the airflow rateuntil the supply airflow rate Vmav reaches the daytime design airflowrate value.

FIG. 5 shows one example of a daytime design airflow rate value and anighttime design airflow rate value. In the example in FIG. 5, duringthe daytime, the supply airflow rate Vmav is set to 2400 m³ per hour,the local exhaust airflow rate Vexv is set to 1080 m³ per hour, theexhaust airflow rate Vgex is set to 1120 m³ per hour, and the offsetairflow rate α is set to 200 m³ per hour. Moreover, during thenighttime, the supply airflow rate Vmav is set to 400 m³ per hour, thelocal exhaust airflow rate Vexv is set to 100 m³ per hour, the exhaustairflow rate Vgex is set to 100 m³ per hour, and the offset airflow rateα is set to 200 m³ per hour.

As an example of changing the supply airflow rate Vmav and the exhaustairflow rate Vgex, there is the case of stopping the supply and exhaustair fans when fumigating another room 100 or when not in use, or thecase of switching from a state wherein the supply and exhaust fans arestopped to a normal operating state, and, initially, a case wherein thesupply airflow rate Vmav is changed due to temperature control.

The room pressure controlling valve (PCV) controlling operations thatare performed in parallel with the operations described above areexplained next. FIG. 6 is a flowchart for explaining the PCV controllingoperation. In the present example, the common exhaust air valve GEXfunctions as a PCV.

The airflow rate stability evaluating portion 204 of the controller 107evaluates whether or not the supply airflow rate Vmav and/or the exhaustairflow rate Vgex is changing (Step S100).

The correction output calculating portion 206 of the controller 107,when there is an evaluation by the airflow rate stability evaluatingportion 204 that the airflow rate is changing (Step S100: YES), readsout, from the control parameter storing portion 208, the PID parameterscorresponding to the airflow rate changing, and sets the PID parametersinternally (Step S101).

On the other hand, the room pressure stability evaluating portion 205 ofthe controller 107, when the evaluation is that there is no change inthe supply airflow rate Vmav nor in the exhaust airflow rate Vgex, andthus that the airflow rate is stable (Step S100: NO), evaluates whetheror not the room pressure (the inside/outside pressure difference) isstable (Step S102). If the absolute value |SP−dPE| of the deviationbetween the setting value SP for the room pressure and the room pressuredPE measured by the differential pressure sensor 109 is within a roompressure stability threshold value (for example, 3 Pa) continuously overat least a room pressure stability evaluating interval (for example, 3seconds), then the room pressure stability evaluating portion 205evaluates that the room pressure is stable, but if the absolute value|SP−dPE| of the deviation exceeds a room pressure variation thresholdvalue (for example, 4.5 Pa) continuously for at least a room pressurechange evaluating period (for example, 30 seconds), then the roompressure stability evaluating portion 205 evaluates that the roompressure is changing.

When there is an evaluation by the airflow rate stability evaluatingportion 204 that the airflow rate is stable and there is an evaluationby the room pressure stability evaluating portion 205 that the roompressure is changing (Step S102: NO), then the correction outputcalculating portion 206 of the controller 107 reads out, from thecontrol parameter storing portion 208, the ND parameters correspondingto the airflow rate being stable, and sets the PID parameters internally(Step S103).

One example of a PID parameter when the airflow rate is changing and aPID parameter when the airflow rate is stable is illustrated in FIG. 7.As is well-known, as PID parameters there are the proportional band P,the integrating time I, and the differentiating time D. When the airflowrate is changing, the proportional band P is 200 Pa, the integratingtime I is 0.1 min., and the differentiating time D is 0 min. On theother hand, when the airflow rate is stable, the proportional band P is200 Pa, the integrating time I is 0.2 min., and the differentiating timeD is 0 min. In the example in FIG. 7, the integrating time I changes toI=0.2 min. when the airflow rate is stable, as opposed to I=0.1 min.when the airflow rate is changing. In this way, the optimal PIDparameters to be applied various control situations are recorded inadvance in the control parameter storing portion 208.

After the PID parameters are set in Step S101 or S103, the correctionoutput calculating portion 206 calculates, through a known PID controlalgorithm, the amount of increase or decrease in the airflow rate Vgexso as to eliminate the deviation between the setting value SP and theroom pressure dPE, to produce a correction control output value so as tochange the exhaust airflow rate Vgex of the common exhaust duct 104 bythe amount of increase or decrease calculated (Step S104).

The summing portion 207 of the controller 107 sums the control outputvalue for the exhaust air, outputted by the exhaust airflow ratecontrolling portion 202, or the control output value for the exhaust airoutputted by the airflow rate changing portion 203, together with thecorrection control output value outputted by the correction outputcalculating portion 206, and outputs the result to the common exhaustair valve GEX (Step S105). If during an airflow balance controllingoperation, then the control output value for the exhaust air, outputtedfrom the exhaust airflow rate controlling portion 202, and thecorrection control output value are summed together, but if during anairflow rate switch controlling operation, the control output value forthe exhaust air, outputted from the airflow rate changing portion 203,and the correction control output value are summed together. In thisway, at the same time as the adjustment to the degree of opening of thecommon exhaust air valve GEX by the airflow rate balance controllingoperation or the airflow switching controlling operation, fineadjustments to the degree of opening of the common exhaust air valve GEXare performed by the PCV controlling operation, to thereby control theroom pressure.

On the other hand, if there has been an evaluation by the airflow ratestability evaluating portion 204 that the airflow rate is stable and anevaluation by the room pressure stability evaluating portion 205 thatthe room pressure is stable (Step S102: YES), then the correction outputcalculating portion 206 suspends the outputting of the correctioncontrol output value calculated by the aforementioned PID controlalgorithm, and continuously outputs the correction control output valuecalculated during the immediately previous calculating period, until acorrection control output value is outputted during a calculating periodthat is after the present calculating period (Step S106).

The correction control output value is summed, as described above, withthe control output value for the exhaust air, and outputted to thecommon exhaust air valve GEX (Step S105), but because here the airflowrate is stable, the correction control output value is also maintainedas-is at its immediately previous value, without the control outputvalue changing from the immediately previous value. Consequently, thecommon exhaust valve GEX is not actuated, and the degree of opening atthat time is maintained.

The processes in Step S100 through S106 are performed repetitively witheach calculating period until the room pressure control is terminated(Step S107: YES).

As described above, in the present example it is possible to reduce thefrequency of actuation of the common exhaust valve GEX while maintaininga constant room pressure, doing so through changing the PID parametersfor the room pressure control when the airflow rate is changing versuswhen the airflow rate is stable, thus making it possible to extend theservice life of the common exhaust air valve GEX. When the airflow rateis changing, then strict control of the airflow rate is necessary inrelation to the changes in the room pressure. Consequently, PIDparameters are used that emphasize rapid responsiveness of the roompressure control, rather than emphasizing the reduction in the frequencyof actuation of the common exhaust air valve GEX. On the other hand,when the airflow rate is stable, then it is possible to maintain aconstant room pressure even without frequent fine adjustments of thedegree of opening of the common exhaust air valve GEX. Given this, PIDparameters that emphasize more greatly a reduction in the frequency ofactuation of the common exhaust air valve GEX, rather than the rapidresponsiveness of the room pressure control, are used when the airflowrate is stable.

Moreover, in the present example it is possible to stop the operation ofthe common exhaust air valve GEX, to further reduce the frequency ofactuation of the common exhaust air valve GEX, by suspending the outputof the correction control output value, to suspend the room pressurecontrol, if the airflow rate is stable and the room pressure is stable.

For safety, in a room pressure controlling system it is important tomaintain a specific room pressure so to avoid an inversion of theinside/outside pressure difference. The system must fulfill thisrequirement, and must be a low-cost, long-life, high-reliability system.In order to reduce the cost of the system it is necessary to useinexpensive valves, requiring service-life countermeasures. In thepresent example, it is possible to reduce the cost of the system throughthe ability to extend the service life of the valve while usinginexpensive valves.

Note that although in the present example the PID parameters for theroom pressure control were changed between when the airflow rate ischanging and when the airflow rate is stable, there is no limitationthereto, but rather the calculating period for the room pressure controlmay be changed between when the airflow rate is changing and when theairflow rate is stable. Specifically, if the airflow rate is changing,then the correction output calculating portion 206 may use, from thecalculating period storing portion 209, a value for the calculatingperiod that more greatly emphasizes rapid responsiveness in the roompressure control than it does the reduction in the frequency ofactuation of the common exhaust air valve GEX, and when the airflow rateis stable, it may read in and use, from the calculating period storingportion 209, a calculating period that more greatly emphasizes areduction in the frequency of actuation of the common exhaust air valveGEX then it does rapid responsiveness of the room pressure control. ThePID calculating period when the airflow rate is stable is longer thanthe calculating period when the airflow rate is changing.

Moreover, in the present example, the common exhaust air valve GEXfunctioned as a PCV; however, the supply air valve MAV may be caused tofunction as the PCV instead. However, when the supply air valve MAV iscaused to function as the PCV, the summing portion 207 during theairflow rate balance controlling operation would sum the control outputvalue outputted by the supply airflow rate controlling portion 201 ofthe controller 106 and the correction control output value outputted bythe correction output calculating portion 206, and output the result tothe supply air valve MAV. Moreover, at the time of an airflow rateswitch controlling operation, the summing portion 207 sums the controloutput value for the supply air, outputted from the airflow ratechanging portion 206, and the correction control output value, outputtedfrom the correction output calculating portion 206, and sends the resultto the supply air valve MAV.

Each individual controller 105, 106, and 107 explained in the presentexample can be embodied through a computer that is provided with a CPU,a memory device, and an interface, and a program for controlling thesehardware resources. The CPU of each of these controllers 105, 106, and107 executes the processes explained the present example through aprogram that is stored in the memory device.

Note that while in the present example a fume hood was used as one localexhaust device, the present invention can be applied also to devicesthat achieve the same role as a fume hood, such as a safety cabinet, andthe like.

The present invention can be applied to room pressure controllingsystems.

The invention claimed is:
 1. A room pressure controlling systemcomprising: a supply air valve regulating an airflow rate for supply airthat is blown into an applicable room; a common exhaust air valveregulating an airflow rate of exhaust air that is drawn from theapplicable room; an airflow rate controller outputting a control outputvalue for the supply air valve and a control output value for the commonexhaust air valve, so as to cause the difference between the supplyairflow rate that is regulated by the supply air valve and the exhaustairflow rate that is regulated by the common exhaust valve to match aspecific setting value, the airflow rate controller measuring afrequency of actuation of each of the supply air valve and the commonexhaust air valve; a differential pressure measuring device measuring aroom pressure that is a pressure difference between an applicable roomand a specific reference room; a correction output calculatorcalculating a correction control output value for a valve that isoperated as a room pressure controlling valve, which is either thesupply air valve or the common exhaust air valve, based on a deviationbetween a room pressure measured by the differential pressure measuringdevice and a specific setting value; a summing device summing thecontrol output value corresponding to the valve that is used as the roompressure controlling valve and the correction control output value, andoutputting the result to the room pressure controlling valve; an airflowrate stability evaluating device evaluating whether or not at least oneof the supply airflow rate and the exhaust airflow rate is changing; anda room pressure stability evaluating device evaluating whether or notthe room pressure measured by the differential pressure measuring deviceis stable, wherein when it has been evaluated by the airflow ratestability evaluating device that at least one of the supply airflow rateand the exhaust airflow rate is changing, the correction outputcalculator performs a control calculation increasing rapidresponsiveness of room pressure control more greatly than reducing thefrequency of actuation of the room pressure controlling valve, and whenthe evaluation is that both of the supply airflow rate and the exhaustairflow rate are stable, the correction output calculator performs acontrol calculation reducing the frequency of actuation of the roompressure controlling valve more greatly than increasing the rapidresponsiveness of the room pressure control, and when it has beenevaluated by the airflow rate stability evaluating device that both ofthe supply airflow rate and the exhaust airflow rate are stable and ithas been evaluated by the room pressure stability evaluating device thatthe room pressure is stable, the correction output calculator continuesto output the correction control output value that was outputted in theimmediately previous calculating period until a time of outputting acorrection control output value in a calculating period that is afterthe current calculating period.
 2. The room pressure controlling systemas set forth in claim 1, further comprising: a control parameter storagestoring a plurality of control parameters for use in calculationprocesses by the correction output calculator, wherein: when it has beenevaluated by the airflow rate stability evaluating device that theairflow rate is changing, the correction output calculator reads out anduses, from the control parameter storage, a control parameter thatincreases the rapid responsiveness of the room pressure control moregreatly than reducing the frequency of actuation of the room pressurecontrolling valve, and when it has been evaluated that the airflow rateis stable, then the correction output calculator reads out and uses,from the control parameter storage, a control parameter that reduces thefrequency of actuation of the room pressure controlling valve moregreatly than increasing the rapid responsiveness of the room pressurecontrol.
 3. The room pressure controlling system as set forth in claim1, further comprising: a calculating period storage storing a pluralityof calculating periods used in the calculating processes of thecorrection output calculator, wherein: when it has been evaluated by theairflow rate stability evaluating device that the airflow rate ischanging, the correction output calculator reads out and uses, from thecalculating period storage, a value for the calculating period thatincreases the rapid responsiveness of the room pressure control moregreatly than reducing the frequency of actuation of the room pressurecontrolling valve, and when it has been evaluated that the airflow rateis stable, then the correction output calculator reads out and uses,from the calculating period storage, a value for the calculating periodthat reduces the frequency of actuation of the room pressure controllingvalve more greatly than increasing the rapid responsiveness of the roompressure control.
 4. The room pressure controlling system as set forthin claim 1, further comprising: a fume hood equipped within theapplicable room; and a local exhaust valve regulating the exhaustairflow rate of the fume hood; and a local exhaust airflow rateregulator controlling the local exhaust air valve so that the planar airspeed of a sash plane of the fume hood is a specified value; wherein:the airflow rate controller outputs a control output value for thesupply air valve and a control output value for the common exhaust airvalve so that the difference between the supply airflow rate that isregulated by the supply air valve and the exhaust airflow rate that isregulated by the local exhaust air valve and the common exhaust airvalve matches a specific setting value.